This project is a neurophysiological investigation of modality-combining properties and mechanisms of multimodal (visual, auditory, somatic) neurons in the superior colliculus of a mammal. The superior attention; vision is a dominant modality of this midbrain structure, but there is also prominent tactile and auditory input. These non-visual inputs are organized similarly to visual input with respect to representation of space. Bimodal neutrons (excited by vision and a non-visual input) have been described, but whether there are specializations to identify and localize objects that excite both modalities at once is not known. I propose to search for and characterize such intermodality specializations. Responses to natural dual-modality objects will be quantified; then by quantifying responses to single-modality stimuli and combinations of them, (with spatial, temporal, and intensity parameters of each modality systematically varied), I expect to learn how the neurons are specialized for responding appropriately to dual-modality objects. This will help to identify the significance and role of multiple modalities of sensory input to the superior colliculus. Among the objectives is to discover whether marginally visible dual-modality objects are better detected or localized than if just vision were present, and whether stimulation in the non-visual modality can attract neural "attention" to the appropriate region of the superior colliculus. Thus, experiments to characterize subthreshold intermodality summation, facilitation, inhibition, adaptation, etc. are planned. Previously, only separate excitation in each modality has been done, thus any modality-combining specilizations have been overlooked. My prior studies in snakes indicate that many specialized intermodality interactions occur in vertebrates, indicating high likelihood of success of this project. The project would advance our understanding of basic function of the superior colliculus, and greatly increase our knowledge of how vision is integrated with other sensory modalities.